There has been a significant increase in the data storage requirements of consumer electronic devices such as digital audio/video players, cell phones, portable universal serial bus (USB) drives and solid state drives (SSDs). This density requirement can be satisfied at relatively low cost by nonvolatile semiconductor memory devices incorporating flash memory, commonly known as flash devices. At present, there are two main types of flash memory, namely NOR flash and NAND flash, and of the two, NAND flash has proven to be especially popular.
However, as flash devices become denser and cheaper, the amount of storage they are expected to provide increases even further. This expectation, in turn, exerts further pressure to render these devices even more dense at an even lower cost costly.